Refrigerant Mass Flow from Capacity and Refrigeration Effect
The mass flow refrigerant-velocity takes as a given, derived.
Example
You enter
- Capacity (tons, or Btu/h if unit set to 0) 5
- Capacity unit 1
- Suction enthalpy h1 (Btu/lb) 180
- Evaporator-inlet enthalpy h4 (Btu/lb) 120
You get
- Refrigeration effect 60 Btu/lb
- Refrigerant mass flow 16.67
- M dot lbh 1000
Details, formula, and sources
m_dot = Q / (h1 - h4), the cooling load over the refrigeration effect off the P-h diagram. A 5-ton system with a 60 Btu/lb effect circulates 16.7 lb/min (1,000 lb/h) - the flow the compressor pumps and a tech hands to the velocity check. Warm the liquid line so the effect drops to 50 Btu/lb and the same 5 tons needs 20% more mass flow, the penalty of poor subcooling. Enter the enthalpies from the P-h diagram; steady flow. An engineering aid; the refrigerant property data govern.
Q_btumin = (unit == tons) ? Q x 200 : Q/60; RE = h1 - h4; m_dot = Q_btumin / RE; m_dot_lbh = 60 m_dot.
The refrigerant mass-flow-from-capacity relation m_dot = Q / (h1 - h4) with the refrigeration effect off the pressure-enthalpy diagram, a standard refrigeration-cycle result, by name.
The mass-flow-from-capacity relation is a public refrigeration-cycle result; the ASHRAE Handbook - Refrigeration covers the P-h cycle.
Estimate. AHJ and licensed professional govern.
Field names used by the API: q, unit_tons, h1_btulb, h4_btulb, re_btulb, m_dot_lbmin, m_dot_lbh
- Mass flow m_dot = Q / (h1 - h4), the load over the refrigeration effectvapor-compression cycle
- Throttling h4 = hf at the condensing pressure (isenthalpic expansion)refrigeration cycle
- Enthalpies read off the refrigerant P-h diagram or tables at the operating state pointsrefrigerant property data